Distributed power train operation supplies motive power from a lead locomotive and one or more remote locomotives spaced apart from the lead locomotive in a train consist. Each lead and remote locomotive includes an air brake control system for controlling braking operations and a communication system for exchanging information between lead and remote locomotives over a communication link. A brake pipe fluidically interconnects each of the locomotives and rail cars of the train wherein modulation of a fluid flow, such as a fluid pressure in the brake pipe, is conventionally used to indicate desired braking operations. Brake application is typically accomplished by venting, or reducing a pressure in the brake pipe. However, brake pipe venting at only the lead locomotive of a train requires propagation of the corresponding brake pipe pressure reduction along the length of the train, thus slowing brake application at rail cars and remote locomotives near the end of the train. In distributed power trains, braking is more effectively accomplished by venting a brake pipe at both the lead and remote locomotives of the train, thus accelerating the brake pipe venting and the application of brakes, throughout the train.
For distributed power trains with an operative communication link between a lead and remote locomotives, wireless traction and braking commands are typically transmitted to each remote unit over the link, such as when a train operator at the lead commands a brake application. For example, in response to a wireless brake application command, each remote locomotive also vents the brake pipe. Similarly, a brake release initiated at the lead is also communicated over the radio link, and each remote may respond by releasing its brakes and charging the brake pipe.
In the event that radio communication becomes inoperable in a distributed power train, a predetermined time period, such as 45 seconds, is typically allocated for attempting to re-establish wireless communications before a communication loss is declared. For example, a remote experiencing a potential communication loss may maintain a last-commanded traction and/or braking condition until the earliest of communications being re-established or the predetermined time period expiring. If the time period expires before communications are re-established, the remote may implement a fail safe mode of operation, such as disabling charging or venting of the brake pipe at the remote, and/or reducing a traction condition of the remote. During this time period the remote locomotive remains responsive to brake pipe fluid flow conditions sensed at the remote locomotive. For example, if a relatively small pressure drop in the brake pipe is sensed, the remote locomotive may interpret the drop as a slow leak and attempt to charge the brake pipe to return it to its previous pressure.